The present invention relates to the field of automated electronic measurement and object identification systems. More particularly, the present invention is directed to methods and an apparatus for the automated determination of certain characteristics of desired reflective objects (such as road signs) and classifying the reflective objects as to the level of retroreflectivity.
Safe motor vehicle travel during low light and nighttime conditions requires that directional, regulatory and cautionary information displayed upon road signs and markers be clearly visible to a vehicle operator traveling at a reasonable velocity down a roadway. Various kinds of reflective sheeting, decals and paints are used on road signs and markers to enhance the readability and perception of information displayed during low light and nighttime conditions. Unfortunately, the effectiveness of these reflective materials tends to deteriorate over time.
Adequate nighttime and low light visibility of roadway signs by vehicle operators is best associated and most impacted with the retroreflectance properties of the individual signs. Retroreflectivity (defined as the ability of a material to reflect incident light back towards its source), specified in candelas per lux per square meter (cd/lux/m2), is an important characteristic utilized by transportation agencies to assess the nighttime visibility of road signs.
Generally, highway and street maintenance departments do not systematically evaluate the deterioration of the reflective materials used on road signs and markers. If inspections of road signs or markers are performed, they are typically accomplished by having inspectors manually position a handheld retroreflectometer directly on the surface of a sign in order to determine a retroreflectivity value for that sign. When there are a large number of road signs or markers (sometimes referred to as traffic control devices or TCDs) in a given jurisdiction, the task of manually inspecting all of these road signs and markers can be time consuming and expensive.
One technique for determining retroreflectivity which does not require that a retroreflectometer be placed directly on a sign is described in U.S. Pat. No. 6,212,480 entitled, xe2x80x9cApparatus And Method For Determining Precision Reflectivity Of Highway Signs And Other Reflective Objects Utilizing An Optical Range Finder Instrumentxe2x80x9d issued Apr. 3, 2001 to Dunne. The Dunne patent relates to a device commercialized by the assignee thereof and marketed as the xe2x80x9cImpulse RMxe2x80x9d retro-reflectometer by Laser Technology, Inc. of Englewood, Colo., U.S.A. In use, handheld devices fabricated according to the Dunne patent are manually directed toward, or precisely at, a target object and then manually xe2x80x9cfired.xe2x80x9d Once fired, the handheld device bounces a laser off the target object and measures the reflected laser energy that is then used to determine a retroreflectivity.
There are several drawbacks of the hand-held laser arrangement described by the Dunne patent. The handheld device can only measure a single color at a time and can only measure one object at a time. The determination of retroreflectivity for a given object is valid only for the actual location, or discrete measurement point, along the roadway at which the measurement was made by the human operator. In order to validate a measurement made by such devices, the device must be taken back to the precise location in the field where an original measurement occurred for a valid comparison measurement to be made.
Another technique established for determining the nighttime visibility of signs has been introduced by the Federal Highway Administration (FHWA). The Sign Management and Retroreflectivity Tracking System (SMARTS) is a vehicle that contains one high intensity flash source (similar to the Honeywell StrobeGuard(trademark) SG-60 device), one color camera, two black and white cameras, and a range-sensing device. The SMARTS vehicle requires two people for proper operationxe2x80x94one driver and one system operator to point the device at the target sign and arm the system. The SMARTS travels down the road, and the system operator xe2x80x9clocks onxe2x80x9d to a sign up ahead by rotating the camera and light assembly to point at the sign. At a distance of 60 meters, the system triggers the flash source to illuminate the sign surface, an image of which is captured by one of the black and white cameras. A histogram is produced of the sign""s legend and background that is then used to calculate retroreflectivity. A GPS system stores the location of the vehicle along with the calculated retroreflectivity in a computer database.
Like the handheld laser device of the Dunne patent, the SMARTS device can only determine retroreflectivity for one sign at a time and can only determine retroreflectivity for the discrete point on the roadway 60 meters from the sign. Two people are required to operate the vehicle and measurement system. The SMARTS vehicle cannot make retroreflectivity determinations for signs on both sides of the roadway in a single pass over the roadway and does not produce nighttime sign visibility information for lanes on the roadway not traveled by the vehicle. Because the system operator in the SMARTS vehicle must locate and track signs to be measured while the vehicle is in motion, a high level of operational skill is required and the likelihood that a sign will be missed is significant.
There are an estimated 58 million individual TCDs that must be monitored and maintained in the U.S. and new TCD installations increase this number daily. For the reasons that have been described, the existing techniques for determining retroreflectivity do not lend themselves to increasing processing throughput so as to more easily manage the monitoring and maintenance of these TCDs. So called automated data collection systems often require that normal traffic be stopped during data collection because either the acquisition vehicle moved very slowly or because the acquisition vehicle had to come to a full stop before recording data about the roadside scene. Furthermore, a human operator is required to point one or more measurement devices at a sign of interest, perform data collection for that particular sign and then set up the device for another particular sign of interest. With such a large number of TCDs that must be monitored, it would be desirable to provide an automated system for determining the retroreflectivity of road signs and markers that addresses these and other shortcomings of the existing techniques to enable a higher processing throughput of an automated determination of the retroreflectivity of road signs and markers.
The present invention provides a system for the automated determination of retroreflectivity values for reflective surfaces disposed along a roadway. An area along the roadway that includes at least one reflective surface is repeatedly illuminated by a light source and multiple light intensity values are measured over a field of view which includes at least a portion of the area illuminated by the light source. A computer processing system is used to identify a portion of the light intensity values associated with a reflective surface and analyze the portion of the light intensity values to determine at least one retroreflectivity value for that reflective surface. Preferably, color images of the area and locational information are also generated by the system and are used together with a characterization profile of the light source to enhance the accuracy of the determination of retroreflectivity values. In one embodiment, a three-dimensional overlay of retroreflectivity values for the roadway is generated and can be manipulated to display retroreflectivity values of a reflective surface at any desired point along the roadway. In another embodiment, a virtual drive through along a roadway is simulated using a plurality of retroreflectivity values to simulate reflections from each reflective surface disposed along the roadway during the virtual drive through.
In contrast to the existing techniques for determining retroreflectivity that require an operator to target individual signs from a known distance, the present invention can determine retroreflectivity without targeting individual signs and can calculate retroreflectivity values at any desired point along a roadway. To overcome the limitations imposed by the existing techniques, the present invention employs several enhancements that are designed to improve the accuracy of evaluating intensity measurements made over a view where the reflective surfaces are not individually targeted and therefore neither the distance to the reflective surface or the normal vector to the reflective surface are known.
In a method in accordance with the present invention, retroreflectivity values for reflective surfaces disposed along a roadway are determined in an automated manner. A light source is strobed as the light source is traversed along the roadway to illuminate an area that includes at least one reflective surface. A plurality of light intensity measurements are collected using at least one intensity sensor directed to cover a field of view which includes at least a portion of the area illuminated by the light source. A computer processing system is then used to identify a portion of at least one light intensity measurement associated with one of the at least one reflective surfaces and analyze the portion of the at least one light intensity measurement to determine at least one retroreflectivity value for that reflective surface.
In a preferred embodiment of the method in accordance with the present invention, a characterization profile for the light source is created for this method. The characterization profile includes an array of known luminance values of reflections of the light source. The characterization profile for the light source is then utilized as part of determining the at least one retroreflectivity value for that reflective surface. Preferably, the array of known luminance values of reflection comprises reflected intensity values for the light source over a range of colors and reflected intensity values over a range of relative angles between the light source and the reflective surface. In one embodiment, a plurality of color images are captured using at least one color camera directed to cover a field of view which includes at least a portion of the area illuminated by the light source. The range of colors of the characterization profile for the light source and the plurality of color images are then used as part of determining the at least one retroreflectivity value for that reflective surface. In another embodiment, locational information is obtained for each of the plurality of light intensity measurements and used to determine a coordinate location for each reflective surface. The range of relative angles of the characterization profile for the light source and the coordinate location are then used as part of determining the at least one retroreflectivity value for that reflective surface. Preferably, a characterization profile of the light intensity sensor is also utilized to further enhance the accuracy of the system. The characterization profile for the intensity sensor preferably includes an array of intensity values of reflections as measured by the intensity sensor in response to a known light source.
A system for acquiring information to assess reflective surfaces disposed along a roadway in accordance with the present invention includes a vehicle and a computer processing system. The vehicle includes at least one high output light source, at least one intensity sensor, at least one color camera, a positioning system, and a control system. The control system is operably connected to the light source, intensity sensor, color camera and positioning system such that the intensity sensor, color camera and positioning system record information associated with an area that includes at least one reflective surface as the vehicle traverses along the roadway in response to repeated illumination of the area by the light source. The computer processor, which may reside within the vehicle or may be located separate from the vehicle, utilizes the recorded information to determine at least one retroreflectivity value for the at least one reflective surface.
In a preferred embodiment of the system, the vehicle further includes a laser scanning system that records distance information including at least a distance between the vehicle and each of the at least one reflective surfaces. The computer processing system utilizes the distance information generated by the laser scanning system to determine at least a normal vector for a face of the reflective surface. Preferably, the high output light source comprises at least two strobe lights arranged to alternatively illuminate the area at an effective strobe rate of at least one flash per second. Preferably, the intensity sensor comprises a black and white camera and the color camera comprises a pair of digital color cameras mounted on the vehicle to generate stereoscopic images of the area. The positioning system is preferably a global positioning system supplemented with an inertial navigation system. In the embodiment in which at least a portion of the computer processing system resides within the acquisition vehicle, at least a portion of the control system is preferably implemented using the computer processing system and a master clock supplied to all of the remaining components of the system to synchronize the system.
In another embodiment of the present invention, a method for displaying and manipulating retroreflectivity data for a reflective surface disposed along a roadway is provided. A plurality of retroreflectivity values for the reflective surface are determined, preferably using the method and system as described. A three dimensional representation of retroreflectivity values of the reflective surface is generated and the three dimensional representation of retroreflectivity values is displayed, preferably as an overlay over a depiction of a roadway. A simulation of the interaction of a vehicle operator/observer is accomplished by generating a simulated vehicle light source and a vehicle operator/observer pair and, for different locations of the simulated vehicle light source and said vehicle operator/observer pair, generating a simulated vehicle operator/observer observation angle and a simulated view of the vehicle pathway which includes the reflective surface. The simulation allows for simulating a changing magnitude of ambient lighting from a first value to a second value, or simulating a change of at least one characteristic of the depiction of the roadway. A corresponding change in the three dimensional representation of retroreflectivity values as a result is determined and also simulated on the display. In one embodiment, the simulation is used to generate a new three dimensional depiction of the reflective surface according to a predictive aging model which includes a gradual degradation of the reflective surface over time. The reflective surface can then be represented and simulated as if the reflective surface exhibited such a gradual degradation in the three dimensional depiction.
In another embodiment, a method for simulating a virtual drive through of a roadway that includes at least one reflective surface disposed along the roadway is provided. A plurality of retroreflectivity values are determined for each reflective surface. A virtual drive through along the roadway is simulated using the plurality of retroreflectivity values to simulate reflections from each reflective surface disposed along the roadway during the virtual drive through. Preferably, the virtual drive through allows for a simulation of a change of at least one characteristic of the depiction of the roadway, such that a corresponding change in the reflections from each reflective surface is determined and simulated. Preferably, the virtual drive through simulates at least one vehicle having a light source and observer pair. In this embodiment, the virtual drive through allows for a simulation of a change of at least one characteristic of the vehicle or light source and observer pair, such that a corresponding change in the reflections from each reflective surface is determined and simulated.